Whenever you use information, you need to evaluate it. The CRAAP method will help you do this.
For web pages, you'll also want to pay attention to the domain, found at the end of the URL. Domains can provide some information on the provider, as well as the purpose. For example, organizational domains (.org) usually exist to present their point of view, or to persuade you. Examples of .org domains: NRA, Right to Life. Commercial domains (.com) exist to provide a service or a product. Other domains: .edu, .mil, .net, .gov.